fix(visitAllArgs): problem with Apollo-Server 2 and Introspection

got error:
Error: The introspection query is resolving asynchronously; execution of an introspection query is not expected to return a `Promise`.

Wrapped type resolvers should maintain the existing execution dynamics of the resolvers they wrap (i.e. async vs sync) or introspection types should be excluded from wrapping by checking them with `graphql/type`s, `isIntrospectionType` predicate function prior to wrapping.

Author: tgerk

README.md

@@ -18,6 +18,10 @@ npm install graphql-middleware-typed-arguments
 - 🛴 Half automatic.
 - 🏆 Works with every GraphQL server.
 
+## Notes
+
+If you would appreciate an integration of the [Yup validation framework](https://github.com/jquense/yup) to validate your scalar and object-type arguments, look at [this package](https://www.npmjs.com/package/graphql-yup-middleware).
+
 ## Demo
 
 The example is taken directly from graphql-middleware-apollo-upload-server which was basis for this generalization.  There are two changes from the original:  the GraphQLUpload type object is imported, but the type name "Upload" could be used as well.  (In fact, type names are simpler way to get at a type defined in SDL.)  The second change is providing the type (object or string) to the middleware factory function provided by this package: `processTypeArgs`.  (The previous version's `upload` method has been preseved and implemented as a special case.)

package.json

@@ -13,7 +13,7 @@
   "repository": "https://github.com/tgerk/graphql-middleware-typed-arguments",
   "author": "Tim Gerk <[email protected]>, Matic Zavadlal <[email protected]>",
   "scripts": {
-    "prepublish": "npm run test",
+    "prepare": "npm run test",
     "test": "npm run lint && npm run build && npm run test-ava",
     "lint": "tslint --project tsconfig.json {src}/**/*.ts && prettier-check --ignore-path .gitignore src{,/**}/{*.ts,*.js}",
     "build": "rm -rf dist && tsc -d",
@@ -44,5 +44,21 @@
   "release": {
     "branch": "master"
   },
+  "homepage": "https://github.com/tgerk/graphql-middleware-typed-arguments",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/tgerk/graphql-middleware-typed-arguments.git"
+  },
+  "bugs": {
+    "url": "https://github.com/tgerk/graphql-middleware-typed-arguments/issues"
+  },
+  "keywords": [
+    "graphql",
+    "middleware",
+    "arguments",
+    "resolvers",
+    "server",
+    "yoga"
+  ],
   "license": "MIT"
 }

src/index.ts

@@ -3,6 +3,7 @@ import {
   GraphQLArgument,
   getNamedType,
   GraphQLNamedType,
+  isIntrospectionType,
 } from 'graphql'
 import { IMiddlewareFunction } from 'graphql-middleware'
 
@@ -46,6 +47,12 @@ function getFieldArguments(info: GraphQLResolveInfo): GraphQLArgument[] {
   return typeFields[fieldName].args
 }
 
+function fieldHasIntrospectionType(info) {
+  const { fieldName, parentType } = info
+  const typeFields = parentType.getFields()
+  return isIntrospectionType(typeFields[fieldName].type)
+}
+
 /**
  *
  * @param type
@@ -153,6 +160,7 @@ export function makeArgumentTransform<T, V>(
     }
 
     return null // exclude arguments when no value provided
+    // (undefined is changed to null, because TypeScript)
   }
 }
 
@@ -212,25 +220,28 @@ export function processTypeArgs<V, T>({
 
 export function visitAllArgs({ transform }): IMiddlewareFunction {
   return (resolve, parent, args, ctx, info) => {
-    const argDefs = getFieldArguments(info)
-    if (argDefs.length) {
-      // Apply argument transform function to all arguments
-      // The caller's transform function is applied to values that may be embedded
-      // in lists and promises, but not to null or undefined values
-      // Finally the resolver is called with transformed argument values
-      return (
-        Promise.all(
-          filterMap(
-            makeArgumentTransform(transform, parent, args, ctx, info),
-            argDefs,
-          ),
-        )
-          // substitute the transformed values into the args object
-          .then(newArgs =>
-            newArgs.reduce((args, newArg) => ({ ...args, ...newArg }), args),
+    // TODO avoid introspection types--very fussy about introducing async into sync code
+    if (!fieldHasIntrospectionType(info)) {
+      const argDefs = getFieldArguments(info)
+      if (argDefs.length) {
+        // Apply argument transform function to all arguments
+        // The caller's transform function is applied to values that may be embedded
+        // in lists and promises, but not to null or undefined values
+        // Finally the resolver is called with transformed argument values
+        return (
+          Promise.all(
+            filterMap(
+              makeArgumentTransform(transform, parent, args, ctx, info),
+              argDefs,
+            ),
           )
-          .then(newArgs => resolve(parent, newArgs, ctx, info))
-      )
+            // substitute the transformed values into the args object
+            .then(newArgs =>
+              newArgs.reduce((args, newArg) => ({ ...args, ...newArg }), args),
+            )
+            .then(newArgs => resolve(parent, newArgs, ctx, info))
+        )
+      }
     }
 
     return resolve(parent, args, ctx, info)